Optical matrix switches, for example, n.times.m optical switches, are capable of connecting one or more input fibers to any one of a number of optical output fibers by reflecting a signal on a selected one of an array of reflective means. Usually an array of parallel input optical fibers are arranged orthogonal to an array of parallel output optical fibers; however these switches are usually bi-directional such that all ports can function as input/output ports. Movable or state changing reflective means are arranged at each of the intersections between the optical paths launched from input and output fibers for selectively coupling a signal from an input fiber to a desired output fiber. Switches of this type are constructed using a wide variety of structures, including mechanical, opto-electronic and magnetic actuation. An n.times.n optical matrix switch of this type requires n.sup.2 reflective means to allow n input ports to be connected to n output ports in a non-blocking fashion.
U.S. Pat. No. 4,988,157 to Jackel et al. herein incorporated by reference, discloses an n.times.m optical matrix switch having slots at 45 degrees to orthogonal waveguides. The slots are filled with a liquid that matches the refractive index of the waveguides. Electrodes positioned adjacent to the slots form gas bubbles in a selected slot by electrolysis. One of the electrodes catalyses the reformation of the liquid from the bubble components when a voltage pulse is applied. Light in the input waveguides is transmitted through an intersection in the presence of liquid, but is reflected into an output waveguide in the presence of bubbles.
Another n.times.m optical matrix switch is disclosed in U.S. Pat. No. 4,580,873 to Levinson. This m.times.n optical switch is formed on a semiconductor substrate. Grooves are etched at the edges of the substrate to accommodate input and output optical fibers so that the output fibers are placed orthogonal to the light paths of the input fibers. At each cross point defined by the input and output fibers, an electromechanically actuated mirror is provided which in one position permits passage of light from its associated input fiber to a subsequent mirror, and in another position deflects the light to its associated output fiber.
Another example of a matrix switch is disclosed in U.S. Pat. No. 5,255,332 to Welch et al. The reflective means in this m.times.n optical switch matrix comprises an array of gratings formed in a semiconductor heterostructure. The gratings have two states. When a refractive index change is induced, the Bragg condition for the light received from an optical signal is met, and a portion of the light is diffracted from the row in which it is propagating into a column toward another optical fiber. In the off state, if the incident light does not satisfy the Bragg condition, the beam propagates unperturbed through the grating to be sampled by a subsequent switch.
Switches vary in size from the minimum 1.times.2 to very large matrixes exceeding 100.times.100.
Today, currently available switching matrices are being manufactured by use of a single stage architecture where both input and output sides of a P.times.P matrix are comprised of 1.times.P rotary switches. A rotary switch of this type is described by Duck et al. in U.S. Pat. No. 4,378,144. Duck et al. propose an arrangement wherein a faceplate comprising a number of collimating lenses along a pitch circle is attached directly to a stepping motor, the shaft of the motor being coaxial with the pitch circle. A rotatable arm with a collimating lens is attached to the shaft for rotation along the pitch circle, with a small distance therebetween, so that the lens of the arm can be optically connected with the lenses on the faceplate when the rotatable arm is moved by means of the shaft of the stepping motor. An optical input fibre is connected to the collimating lens (hereafter called a lens-to-fibre unit) of the arm and a plurality of optical output fibres are attached to the respective collimating lenses on the faceplate for a switching operation when the rotatable arm moves from one position to another.
Configuring a plurality of 1.times.P rotary switches into a single stage P.times.P switch has the following limitations:
a) the cost of the switch is largely dependent upon the cost of the number lens-to-fibre units required; and,
b) The maximum reconfiguration time of the component 1.times.P rotary switch is directly dependent upon the dimension of the matrix.
It is usually preferable that optical switches be efficient, fast and compact. As telecommunication networks have evolved over the years and have become more complex, a need has arisen for a matrix switching system capable of optically coupling any one of a large number of other fibers to another. Furthermore, it is desirable for the switching system to be "non-blocking", i.e. the switching of one input fiber to an output fiber should not interfere with the light transmission of any other input fiber to any other output fiber.
Another type of 1.times.n optical switch has been disclosed by Laughlin in U.S. Pat. Nos. 5,555,327 5,444,801 5,333,175, 5,555,558 and 5,566,260 wherein one input is switched to any of a plurality of output locations or ports by placing a wedged shaped block of glass next to a prism. Although Laughlin's switch may be useful, it appears to have several drawbacks. For instance, the output beams that exit Laughlin's prism are non-parallel and non-orthogonal to the prism face that they exit. It is believed that the coupling of the light exiting at different angles is somewhat difficult. Furthermore, if Laughlin's wedge is moved slightly out of position so that a beam incident upon the wedge goes through a thicker or thinner portion than expected, the beam will not exit exactly where the light is being collected.
This invention obviates many of the potential problems associated with Laughlin's disclosed invention.
It is an object of this invention to provide an n.times.n optical switch, that for numbers of n exceeding for example 4, would require less than n.sup.2 optical switching elements.
It is also an object of this invention, to provide an optical switch that wherein a standard gate can be used for each switching element, and wherein the switch requires less than n.sup.2 optical switching elements to configure an n.times.n switch for n&gt;8.